Field
Embodiments relate to an odor detection system, an odor identification device, and an odor identification method for patterning an odor itself and identifying the odor. Embodiments also relate to a sensor used in the system. Moreover, embodiments relate to a device used in the sensor.
Description of the Related Art
An odor is identified as odor information (sensory information) when various chemical substances simultaneously and compositively act on olfactory cells. Meanwhile, in sensing odor most are intended to detect and measure a specific gaseous chemical substance related to an odor from a chemical substance group constituting the odor (hereinafter, also referred to as odor factor).
A chemical sensor, such as an ammonia sensor, a hydrogen sulfide sensor, or the like, is often used where such sensors are designed to specify a chemical substance among chemical substances constituting an odor or to measure an individual odor causative substance, for example, an odor causative substance having a specific odor such as ammonia, mercaptan, aldehyde, hydrogen sulfide, or amine.
The sensor forms a surface state having a physical and chemical selectivity with respect to a specific molecule, and measures the specific substance by using a change in surface state when the specific molecule reacts with the surface or is adsorbed to the surface, or separates and then measures a specific odor causative substance by using a means for separating a chemical substance such as an adsorption column, for example, by using a chromatography method.
As a sensor system which can be used in separation and measurement of individual odor causative substances as described above, a sensor system in which a surface plasmon (SPR) generated by interaction of metal nano-particles with laser light is used in a detector portion, a sensor system using a field-effect transistor in which source, drain, and gate electrodes are provided on semiconductor silicon and a molecule selection film is formed on the gate and which uses adsorption of a substance to the surface, a surface acoustic wave sensor measuring and detecting a change in propagation velocity of a surface acoustic wave due to adsorption of a substance to the surface, or a QCM sensor using a variation in resonant frequency of a quartz oscillator according to the weight of a substance attached to the surface.
As a conventional odor sensor, generally, a thin film having substance selectivity is formed on the surface of a detector in the sensor system and a specific substance which causes the odor is detected by the thin film.
There is also a sensor using a change in carrier density according to oxidation-reduction reaction of oxygen on the surface of a metal-oxide semiconductor set to a high temperature. However, in this sensor, oxidation reaction of a reducing substance occurs on the surface, and thus the surface cannot be coated with a film or the like having substance selectivity and only reducing substances can be measured. Therefore, this sensor is only effective for limited odor substances such as ammonia and hydrogen sulfide.
Meanwhile, regarding a sensor using a quartz oscillator or the like, an array-type odor sensor is disclosed in which a plurality of quartz oscillators are provided (for example, see Japanese Patent No. JP 4737726 B2).
In this sensor, by providing the plurality of quartz oscillators to be arranged in a specific direction with respect to a substrate, a large amount of gas containing a substance to be detected can efficiently contact a sensor unit and thus detection efficiency is improved.
In non-patent literature, Tokyo Institute of Technology Laboratory Publication LANDFALL Vol. 39, p. 19-22, April 2000 (http://silvia.mn.ee.titech.ac.jp/system.html) (“TITL”), there is an attempt to specify an odor by performing multivariate analysis using a plurality of sensors. In this case, a sensor system to be used is configured by a combination of monofunctional sensors that measure a specific chemical substance defined in advance. Thus, when a substance constituting the odor is already known, the odor can be expressed by multivariate analysis.
Recently, there is also an attempt that, when a plurality of luminescent molecules each responding to molecules having different polarities are applied onto a substrate and then exposed to an odor factor in order to detect and evaluate an odor itself as well as to detect and measure a specific substance constituting an odor as described above, the substrate emits light in a specific pattern in response to the odor, and then this pattern is captured and recorded to image the odor (for example, see SCOPE Project (http://o.ed.kyushu-u.ac.jp/SCOPE/Welcome. html) (“Scope Project”).
In this odor imaging system, a multiple probe film is used in which particles obtained by combining compounds each identify a plurality of odors, for example, fluorescent nanoparticles for detection are arranged.
With such a configuration, when particles each are bonded with specific odor factors, the particles emit light and the light-emitting particles can be visualized by capturing them with a CCD camera or the like.
However, the aforementioned conventional sensor can only detect, for example, information related to substances having specific molecular structures on the basis of existence or level of an electrical resistance value or combination of prescribed substances and can only define odor causative substances (molecules) specified by the molecular structures, molecular weights and the like of the substances. Thus, even though the presence or absence of the substances can be detected, it is difficult to detect and identify odor information obtained by using olfactory sense of human beings such as an olfactory test as measurement results.
Non-patent literature, e-nose Instruments co., Ltd. homepage http://e-nose.co.jp/product00.html, also discloses an odor sensor, however, only detection and quantitative determination of a specific molecule can practically be performed by the level of oscillation frequency corresponding to the specific molecule.
In multivariate analysis disclosed in TITL, it is necessary to prescribe in advance the substance to be measured by each individual sensor used as sensors, and thus an odor configured by a substance which is not assumed by each sensor cannot be accurately expressed.
That is, since an odor has generally a complicated configuration formed from a plurality of chemical substances, there is a problem in that it is difficult to acquire or express odor information only by combination of mono-functional sensors each defining a specific object to be measured which is included in a certain odor.
In order to solve such a problem, in the method of SCOPE Project described above, light emitted from a fluorescent substance is captured. However, an excitation light source, CCD camera and the like are necessary for light emission is needed. Thus, in this case, a device itself would be larger and it is difficult to easily define and identify an odor.